The present invention relates to a method of automatically adjusting thread tension in a sewing machine.
The prior art belonging to this field will be explained in reference to the attached drawings. With respect to the thread tension, taking the tension of the upper thread, for example, it is preferable to make adjustments for thin fabric materials, middle materials and thick materials in proper ranges of the thread tension as shown with arrows in FIG. 1. It is in general required to increase the tension as thickness of the fabric becomes large and as hardness becomes high.
For automatically responding to these characteristics of the fabric, there has been proposed an adjustment of an electric driving part of the thread tension device in accordance with the data of the fabric thickness. However, for the fabric hardness, there have not been any measures.